1. Field of the Invention
This invention relates to transceivers and particularly, though not exclusively to FMCW radar transceivers operable in the millimeter waveband.
2. Discussion of Prior Art
A radar system generally requires a means for separating the transmitted signal from the received signal.
This can be achieved by using separate transmit and receive antennas. However, space limitations often make this option undesirable.
An alternative option is to employ a duplexer, which is a device that allows a single antenna to be used for both the transmitter and receiver.
A CW system requires the transmitter to be active simultaneously with the receiver, so the duplexer must separate and isolate the transmitted power from the receive port of the radar. Known ways of achieving this include the use of a hybrid junction, a circulator or a polarizer to split the signals.
FMCW systems also require a local oscillator (LO) signal for demodulating the received signal. One method of generating the LO signal relies on tapping off a portion of the transmitted signal.
See for example EP-A-185,446, which discloses a duplexer in which a portion of the transmitted signal is tapped off by means of a field-distorting probe.
The use of a probe does have certain disadvantages however; manufacture is difficult and the disturbance it causes to the transmitted signal can impair the overall performance of the transceiver.